"Many people have heard that Americans are getting heavier," said the study's lead author Joyce Lee, a pediatric endocrinologist at the University of Michigan's Mott Children's Hospital and assistant professor in the Department of Pediatrics and Communicable Diseases.

"Our research indicates that higher numbers of young and middle-age American adults are becoming obese at younger and younger ages," Lee said.

Researchers in the federally-funded study used data on children and adults born between 1926-2005.

They found that 20 percent of those born between 1966-1985 were obese by ages 20-29.

But data indicated that the older the generation, the later in life obesity took hold. Among those born between 1946-1955, obesity was not reached until ages 30-39. Obesity prevalence was even later for those born between 1926-1935.

Researchers also found these trends were worse for certain minority populations. "What is particularly worrisome is that obesity trends are worse for blacks compared to whites," Lee said.